Fries, photoproducts reaction

If the photo-Fries reaction would occur via a concerted mechanism, the absence of solvent should be of minor importance for the formation of rearranged products. However, conclusive evidence supporting the radical pair mechanism arises from the experiments carried out with phenyl acetate (10) in the vapor phase. The major product in the irradiations of 10 is phenol (13), which accounts for 65% of the photoproducts. Under these conditions, less than 1% of ortho -hydroxyace-tophenone (11) appears to be formed [19,20]. Conversely, when a high cage effect is expected, as in rigid matrixes (i.e., polyethylene), the result is completely different, and phenol is practically absent from the reaction mixtures [29]. In the intermediate situation (liquid solution), both rearranged products and phenol are formed in variable amounts depending on solvent properties. These observations... 

When the crystal of 59c was irradiated at 0°C, a single regioisomer of 60c was obtained quantitatively. The photoproduct 60c showed an ee of 42%. Furthermore, a higher ee value of 60c (87% ee) was obtained in the reaction at -50°C. The radical mechanism has been confirmed in the photo-Fries rearrangement of aromatic amides. 

Aromatic polyurethanes exhibit a strong tendency to yellow in sunlight. This may be accounted for by two mechanisms based on formation of different photoproducts. The first one was found to be a photo-Fries reaction caused by a short wave length light [572]. The second one, caused by longer wave length light, is formation of quinonoid structures [573] ... 

The photoproducts, [2]catenanes 37 and 38, contain two disconnected rings since the photochemical reaction leads to decomplexation of the bpy chelate from the ruthenium(II) centre, fri a typical reaction, a degassed CH2CI2 solution of 38 and NEt4. cr was irradiated with visible Ught, at... 

---